1. Field of the Invention
The present invention relates to a material film for a mask film, a process for producing a mask film using the material film and a process for producing a printing plate of a photosensitive resin. More particularly, the present invention relates to a material film for a mask film advantageously used for preparation of a mask film which is used for preparation of a printing plate of a photosensitive resin such as a flexographic printing plate, wherein a resin layer not transmitting ultraviolet light in the material film exhibits uniform transparency at portions the color of which are eliminated by irradiation with laser beams and suppresses formation of scratches, and the mask film can be easily positioned in preparation of great printing plates and, in attaching with the printing plate material, can easily be attached at the entire surface and suppresses formation of bubbles; a process for producing a mask film using the material film; and a process for producing a printing plate of a photosensitive resin using the mask film.
2. Description of Related Art
Printing plates of a photosensitive resin such as flexographic printing plates, which are formed by irradiating a photosensitive resin layer of a printing plate material having the photosensitive resin layer with light through a mask film used as a negative film having a desired pattern, followed by removing portions of the photosensitive resin layer not exposed to the light by washing, have heretofore been known.
The mask film used for preparing the printing plate of a photosensitive resin is produced, in general, in accordance with a photographic process using silver salts or various printing processes such as a process using a laser printer. However, these processes cannot be used for preparing a mask having a great size. For example, when a mask having a great size such as the size of news paper is required, two or more mask films are used and combined together in a manner such that an image is formed without discrepancy. Moreover, the photographic process has a drawback in that procedures are complicated since the operations must be conducted in a dark room specific for the photographic process and treatments with a plurality of chemicals are required although the photographic process provides excellent resolution. On the other hand, in the case of the printing process, the operation is simple since a pattern can be formed directly by a printer using digital data. However, the process provided by ZANTE Company (a United States company) using a laser printer has drawbacks in that a treatment with a chemical is necessary to improve the property of a mask film not transmitting light and, moreover, the resolution is not sufficient.
As the technology using laser beams in the field of preparing printing plates, for example, a resin printing plate having depressed portions for printing which are formed by irradiating desired portions of a resin layer in a printing plate material having the resin layer on the surface with laser beams so that the desired portions of the resin layer are sublimed or decomposed (for example, Japanese Patent Application Laid-Open No. Heisei 5(1993)-24172) and a printing plate which is formed, using a resin printing plate material having a resin layer sensitive to ionizing radiation and a layer not transmitting ionizing radiation disposed on a substrate, by removing portions of the layer not transmitting ionizing radiation corresponding to a printing image by irradiation with laser beams, followed by irradiating the portions of the resin layer sensitive to ionizing radiation corresponding to the portions removed above with ionizing radiation and then by subjecting the portions of the resin layer sensitive to ionizing radiation irradiated above to a development treatment (for example, Japanese Patent Application Laid-Open No. Heisei 10(1998)-67088), have been disclosed.
However, in the above technology, a printing plate is prepared by directly irradiating a resin printing plate material with laser beams without using a mask film, and the technology is not related to the production of a mask film.
Under the above circumstances, the present inventors proposed a technology providing a material film for a mask film which is advantageously used for producing a mask film used for preparing a printing plate of a photosensitive resin such as a flexographic printing plate, does not require treatments with chemicals, provides excellent resolution by etching with laser beams and can be used for preparing a printing plate having a great size, and a process for producing a mask film using the material film (for example, Japanese Patent Application Laid-Open No. 2003-215777).
However, although the mask film obtained by using the above material film for a mask film has the advantageous properties described above, the mask film is not always satisfactory due to drawbacks in that an unevenly coated layer of the resin layer not transmitting ultraviolet light tends to be formed which directly causes fluctuations in the transmission of light in the portion the color of which is eliminated with leaser beams, that scratches are formed in the resin layer not transmitting ultraviolet light. Furthermore, in the preparation of printing plates having a great size, difficulties due to excessively strong attaching between the printing plate material before the irradiation and the resin layer not transmitting ultraviolet light arise, for example, in positioning of the mask film with the printing plate material or in removing the contained air in some portions between the printing plate material and the resin layer not transmitting ultraviolet light resulting in insufficient contact between the mask film and the printing plate material which results in that a precise printing plate cannot be obtained since the irradiation is conducted while the printing plate material and the mask film are not sufficiently attached to each other.
For the material film for a mask film, a resin layer not transmitting ultraviolet light exhibiting improved scratch resistance and adhesion with the substrate film has been desired so that the resin layer not transmitting ultraviolet light does not have scratches or is not peeled from the substrate film during handling of the material film and during working.